Preparing Slides

Cavity Well Slides
I use cavity well slides which have a shallow circular indentation in their center which can be filled with fluid. I make these slides with a slightly weak 'normal' saline solution of a around 5ml table salt (one level teaspoon) to a litre of deionised water.

The cavity is filled with the solution until it stands up above the top of the cavity. I then drag a fingertip blood drop through the solution and mix it into the water. A new coverslip is carefully placed to avoid getting a bubble in the sample. With gentle pressure and careful blotting the coverslip settles and seals the solution in the cavity. The coverslip moves easily at first but once it is settled and has been left for 10 minutes it is quite secure.

I have found placing the coverslip can be quite tricky so I usually make 2 or 3 slides at the same time and usually get one that is good. A small bubble in the sample is not always a problem so I still keep these slides to look at.

I have sometimes found that too much of the blood drop settles into the middle of the cavity. If this happens I store the slide propped upside down for a day or two. This spreads the blood cells over the coverslip where they can be easily observed.

This type of cavity slide can keep blood for a long time - I've observed bacteria in this kind of slide that was 4 weeks old. The disadvantage is that there is a limited viewing area. Trying to focus on subjects deep within the cavity risks breaking the coverslip and damaging the objective lens. Much of the sample in the cavity is too dense for viewing anyway. It is better to scan round the edge of the cavity where the sample is a suitable depth. In this area there are convenient spaces between the blood cells where the bacteria are more easily seen. This is actually quite a broad area and usually provides plenty to look at.

NEXT: Observing with the Microscope

Or back to: Introduction